Conventional multiple disc clutches and/or brakes employed in a drive train establishing device for a vehicle transmission generally include one or more clutch disc packs consisting of a plurality of engagable clutch plates having teeth on the periphery thereof and alternating with clutch separator plates having similar teeth on the periphery opposite to the teeth of the clutch plates. Thus, one set of plates are splined to an encompassing clutch drum or stationary member while the alternating set of plates are splined onto a central shaft or ring.
Prior efforts to improve the frictional characteristics of the clutch or brake resided in improvements in the characteristics of the friction lining for the clutch plates or discs, and substantially no attention had been paid to the frictional characteristics of the separator plates. As the friction linings for more recent clutch discs have been formed utilizing a resin-impregnated, paper-based friction material, the separator plates should not be formed of a material or have a surface texture which will cause undue wear of the lining.
For separator plates interleaved between the clutch plates that have suitable friction linings on the opposite surfaces thereof, the steel separator plates are conventionally finished by a tumbling process. To enhance the frictional characteristics of the separator plates when used in conjunction with the friction-lined clutch plates, it was suggested to alter the surface characteristics of the steel plates. Various surface preparations and procedures were tried, such as sandblasting, shot peening and knurling; however, the resulting surfaces either did not increase the coefficient of friction or caused undue wear and/or damage to the friction lining of the mating clutch disc faces.
Also, coating of the tumbled separator plates with a wear-resistant material was tried, but increased wear of the friction lining resulted. As an example, the steel plates were sputter-coated with a layer of titanium nitride, a material known for its wear resistant capabilities for tool bits, saw blades, etc. Although a slight increase may have been detected in the coefficient of friction, this was clearly offset by a substantial increase in the wear of the friction lining. The present invention solves the problem of increased wear of the friction linings while significantly enhancing the coefficient of friction for the clutch separator plates.